1. Field of the Invention
This invention relates to an epoxy resin composition, and more specifically, to an epoxy resin composition which has excellent properties, above all high water resistance, chemical resistance and heat resistance, and is suitable for use as a paint, a casting material and a molding material for making laminated plates.
2. Description of the Prior Art
It has been known that compositions comprising bisphenol A-type epoxy resins or halogen-containing bisphenol A-type epoxy resins and curing agents such as aromatic polyamines, amine adducts, dicyandiamide, acid anhydrides or phenol novolak resins are used as paints, molding materials and casting materials, and such compositions may be formed in varnishes by using solvents to use them for molding laminated plates by impregnation in reinforcing substrates.
In recent years, insulating paints, encapsulating materials and laminated plates (printed circuit boards) in electrical and electronic component parts have required increased heat resistance in order to increase the reliability of mechanical properties and electrical insulation at high temperatures. Paints, encapsulating materials and laminated plates (printed circuit boards) made from conventional bisphenol A-type epoxy resins or halogen-containing bisphenol A-type epoxy resins have the defect that their glass transition temperature (Tg) is still low, and at high temperatures, their mechanical strength and electrical insulation are reduced. Polyfunctional epoxy resins such as a phenol novolak type epoxy resin or an o-cresol/novolak type epoxy resin are added to the above epoxy resins in order to increase their heat resistance. Use of large amounts of the polyfunctional epoxy resins reduces the heat shock resistance of the above epoxy resin although it does result in an improvement in heat resistance. Consequently, cracking tends to occur in the paints and encapsulating materials. When the laminated plates are treated in a solder bath after boiling treatment, phenomena called "blister", "peel", "measling" and "crazing" are sometimes observed in the laminated plates treated.
It has been strongly desired therefore to provide an epoxy resin composition which does not undergo significant deterioration in mechanical strength and electrical insulation even at high temperatures and has excellent heat shock resistance.